1. Field of the Invention
This invention relates to nucleic acid probe molecules of hairpin-shaped structure and methods for detecting nucleic acids using the probe.
2. Description of the Prior Art
A variety of nucleic acid detection methods has been applied to a diagnosis of diseases, judgement of a species of animals and plants, judgement of parents and children, DNA cloning and the like. The prior art of detecting nucleic acid includes a method employing labeled probes, such as Southern hybridization. A variety of improvements have been made in these methods.
An example of the improvements is a target DNA detection method, wherein by an enzymatic reaction using RecA proteins, a recombination intermediate is formed between a target DNA and an oligonucleotide used as a probe (Cheng et al., J. Biol. Chem. 263, 15110-15117, 1988). However, the intermediate is unstable, especially after deproteinization. Therefore, Cheng et al. formed a stable recombination intermediate using light bridging. However, the light bridging causes non-specific binding of the probe to a target DNA and a damage of the target DNA due to the ultraviolet irradiation during the light bridging.
Another improvement has been also known, wherein the defects inherent to the prior art described above can be partially solved. This improvement is use of a padlock-shaped oligonucleotide probe, wherein both ends of the probes are hybridized to the adjoining sequences in a target DNA, and then both ends of the probe are ligated to form a more stable hybrid (Nilsson et al., Science, 265, 2085, 1994). Yet, in this method, the target nucleic acid molecule must be single strand. Therefore one cannot perform analysis of a double strand DNA such as genomic DNA.